what's this then?
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whats this then
slowrotor. Yes. I have been researching this system for the last twelve months. The objective was to determine whether it was possible to increase inertia without placing unacceptable loads on the blades, and without the necessity to have a heavy hub to carry the centrifugal forces. I have also during the development managed to reduce the tip loss factor quite dramatically. I am in the process of manufacturing a full size rotor system which i will be testing during next summer. Bug
as long as it comes in at under 10k, i'm sure it will be a hit.
Bugdev, I would like to make a wager with you that it'll never get certificated. Call me cynical but with EASA these days and the rest of the aviation system we have nowadays, a new 'type' isn't going to be easy to certify.
Bugdev, I would like to make a wager with you that it'll never get certificated. Call me cynical but with EASA these days and the rest of the aviation system we have nowadays, a new 'type' isn't going to be easy to certify.
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Hmmm, good concept.
BugDevHeli,
That ring rotor is the business!
I mentioned the possibility on Rotorheads a while back, since Bell apparently tried it in a tail rotor - the response at the time was that the aerodynamicists would fall about laughing. 
The way they work is clever. Normally the tip vortex gets washed away with the downwash, but the ring traps the vortex to rotate about it's circumference. The final result is that the airflow looks more like it would in a fenestron (30% effective radius increase), but without the weight penalty. The ring doesn't even need to be that stiff, since centrifugal force (by centripetal acceleration) takes care of shape. The rotor behaves like the theoretically ideal case of an infinite number of slender rotors.
I looked up some figure of Merit stuff in Prouty recently, and have come to some interesting conclusions. The number of blades is (all things being equal) chosen to keep the blade aspect ratio about 20:1 from memory. In fact a high solidity ratio is beneficial for hover figure of merit, and ring rotors will benefit from this. This will be equally true in forward flight, since Nr may be kept relatively slow. However, I would carefully investigate how forward flight affects the ring trapped vortex stability before going too far.
I have some other questions about the "delta3" trimmer, since i imagine you will eventually be aiming the ring rotor at a rigid head. Have you had to chose a specific Nr to get wee-wa d3 and coning d3 the same? I asked this since Comanche had variable "delta3" ( with d3=fn(Nr,Lock No.) ) although the 15% effective hinge offset would suggests ~10 degrees d3 (i use quotes because in both cases the change is affected by control system not head geometry). Since wee-wa is a result of rotor gyroscopic behaviour, increasing Nr will cause increased d3 correction. Since rotor coning is a result of rotor out of plane geometry, increasing Nr will cause reduced d3 correction. Since you are using R22 components i imagine 18 degrees is your starting point, but have you had to play with Nr for it to work?
I imagine you to be very familiar with rotor dynamics, i figured it from reading Frank Robinson's and Nick Lappos' stuff anyhow!
Mart
That ring rotor is the business!
I mentioned the possibility on Rotorheads a while back, since Bell apparently tried it in a tail rotor - the response at the time was that the aerodynamicists would fall about laughing. The way they work is clever. Normally the tip vortex gets washed away with the downwash, but the ring traps the vortex to rotate about it's circumference. The final result is that the airflow looks more like it would in a fenestron (30% effective radius increase), but without the weight penalty. The ring doesn't even need to be that stiff, since centrifugal force (by centripetal acceleration) takes care of shape. The rotor behaves like the theoretically ideal case of an infinite number of slender rotors.
I looked up some figure of Merit stuff in Prouty recently, and have come to some interesting conclusions. The number of blades is (all things being equal) chosen to keep the blade aspect ratio about 20:1 from memory. In fact a high solidity ratio is beneficial for hover figure of merit, and ring rotors will benefit from this. This will be equally true in forward flight, since Nr may be kept relatively slow. However, I would carefully investigate how forward flight affects the ring trapped vortex stability before going too far.
I have some other questions about the "delta3" trimmer, since i imagine you will eventually be aiming the ring rotor at a rigid head. Have you had to chose a specific Nr to get wee-wa d3 and coning d3 the same? I asked this since Comanche had variable "delta3" ( with d3=fn(Nr,Lock No.) ) although the 15% effective hinge offset would suggests ~10 degrees d3 (i use quotes because in both cases the change is affected by control system not head geometry). Since wee-wa is a result of rotor gyroscopic behaviour, increasing Nr will cause increased d3 correction. Since rotor coning is a result of rotor out of plane geometry, increasing Nr will cause reduced d3 correction. Since you are using R22 components i imagine 18 degrees is your starting point, but have you had to play with Nr for it to work?
I imagine you to be very familiar with rotor dynamics, i figured it from reading Frank Robinson's and Nick Lappos' stuff anyhow!
Mart
Last edited by Graviman; 7th Dec 2006 at 19:39. Reason: Typos.
Developments
Bug et al,
As you know I am a big fan of anyone attempting to pioneer anything that will improve the performance and safety of helicopters; kit built or otherwise and I thoroughly commend your progress to date. However, there is one glaringly obvious question that must be asked:
Why bother, attempting to pioneer new risky technologies on a machine where the cost (both purchase and operating) is the key market driver. There are few (if any) serious contenders for low-cost lightweight single and twin seat helicopters on the market anywhere. Why not use your engineering know-how to produce a £15K safe single seater and a £30K safe two seat recreational helicopter? Think of the number of people that you could sell to then... With a sufficiently simple machine there might even be a case for a NPPL(H)!
CRAN
As you know I am a big fan of anyone attempting to pioneer anything that will improve the performance and safety of helicopters; kit built or otherwise and I thoroughly commend your progress to date. However, there is one glaringly obvious question that must be asked:
Why bother, attempting to pioneer new risky technologies on a machine where the cost (both purchase and operating) is the key market driver. There are few (if any) serious contenders for low-cost lightweight single and twin seat helicopters on the market anywhere. Why not use your engineering know-how to produce a £15K safe single seater and a £30K safe two seat recreational helicopter? Think of the number of people that you could sell to then... With a sufficiently simple machine there might even be a case for a NPPL(H)!
CRAN
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whats this then.
slowrotor. heres a brain teaser for you. centrifugal force wants to pull the blades off. If the blades are retained by a ring are the blades still pulling directly on the hub, or are they now pushing on the ring? if they are pushing on the ring where is the load going then? Now consider that they both pull on the hub and push on the ring? Another little anomoly of course, no lead lag!
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Bug,
Sure, that makes sense. But the ring is stressed in tension, same as any normal blade, so I am not sure that a ring is any better than direct tension to the hub.
I do think the ring has merit for lead lag as you suggest, and preventing flutter with multiple light blades.
I have a small RC model with a tip ring and very light duty blades, it can hit things without harm.
The ring could be a wire if the load is pure tension.
Sure, that makes sense. But the ring is stressed in tension, same as any normal blade, so I am not sure that a ring is any better than direct tension to the hub.
I do think the ring has merit for lead lag as you suggest, and preventing flutter with multiple light blades.
I have a small RC model with a tip ring and very light duty blades, it can hit things without harm.
The ring could be a wire if the load is pure tension.
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whats this then.
slowrotor. When you surround the blades with a ring centrifugal force from the end of the blade is contained and redirected around the ring itself, the blades now have a certain ammount of pull on the hub and a certain ammount of push on the ring. Depending on the elasticity of the ring it is possible to put what ammount of centrifugal force you rquire on the hub itself. It is therefore possible to add as much weight to the ring to give the inertia required without loading the hub as is the case if you simply add tip weight to a conventional rotor blade. Regards Bug
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BugDevHeli,
This sounds like the turbine blade/disk vs blisk problem, if you want to do some viability homework. The secret is to minimise the mass in the ring, so that there is enough hoop stress left over to take some blade centrifugal "pressure" distribution. Then load can be shared between hub and ring.
Don't forget that if you are eventually going for the benefits of rigid rotor, only the hub can transfer the bending moments. The stabilising force keeping the blades in plane will also not be generated by the ring.
I remember a conversation with a colleague who had spent some time at Rolls. The ring in a blisk is more for aerodynamic reasons, to stop backflow leakage, and is only really strong enough to take it's own weight.
Don't take my word for this, but at least convince yourself the concept is right. If it is then best of luck keeping the tradition of innovation alive!
Mart
This sounds like the turbine blade/disk vs blisk problem, if you want to do some viability homework. The secret is to minimise the mass in the ring, so that there is enough hoop stress left over to take some blade centrifugal "pressure" distribution. Then load can be shared between hub and ring.
Don't forget that if you are eventually going for the benefits of rigid rotor, only the hub can transfer the bending moments. The stabilising force keeping the blades in plane will also not be generated by the ring.
I remember a conversation with a colleague who had spent some time at Rolls. The ring in a blisk is more for aerodynamic reasons, to stop backflow leakage, and is only really strong enough to take it's own weight.
Don't take my word for this, but at least convince yourself the concept is right. If it is then best of luck keeping the tradition of innovation alive!
Mart
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I think the ring would require more material to resist the outward force than a direct to hub tension rod.
Think of a high wire circus act. The force of a 170lb performer on the wire puts several thousand pounds of tension in the wire. On the other hand, a small wire could lift the performer straight up with just 170lb tension.
Sorry, I don't think the ring is better.
Think of a high wire circus act. The force of a 170lb performer on the wire puts several thousand pounds of tension in the wire. On the other hand, a small wire could lift the performer straight up with just 170lb tension.
Sorry, I don't think the ring is better.
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whats this then
Slowrotor,Graviman Thanks for constructive feedback. I dont want to give too many details on prune about the ring construction or tiplets and it has just cost me a small fortune the pay for the fluid dynamic analysis. What i can say is that the ring has a special profile that minimises airflow disruption during foreward flight and if sufficiently rigid in the horizontal axis to remove any blade flutter,or lead lag. The blades on my ring rotor adopt a different shape compared to conventional blades when under coning loads. the blades cone near the hub but go horizontal near the tips. As a side issue the rotor is very quiet more of a hum than a whop whop. Music to the ears! Based on the model it is possible to produce a rotor giving as much lift as a 22 having 5 times the inertia and being a little over half its weight.
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BugDevHeli,
Your post already tells me you are very serious about this concept. I understand what you are saying about the construction required to keep the tips horizontal, but out of respect for your commercial rights will not comment further. Very clever idea.
I imagine the ring aerodynamically performs well with forward flight climb/descent and with gusts?
I wish you every success with this concept. I imagine you have a flight test program planned out for either the full size or the scale model. My experience with computer simulation (my specialisation is FEA) is that it is very good for establishing viability or comparing two alternates. The final performance will never be quite what the computer predicts, since the code is based on linear mathematical ideals. Testing is the only way to prove both the aerodynamics and the structure.
You may have hit the timing right on the head. Sikorsky will soon be demonstrating the X2, which is based on rigid rotor technology. Once you have test data to prove out your idea, i would seriously consider approaching them for either a technology development or licensing budget. I really can't comment about other manufacturers, since i gained any heli knowledge from the "local" Sikorsky representative.
Mart
Your post already tells me you are very serious about this concept. I understand what you are saying about the construction required to keep the tips horizontal, but out of respect for your commercial rights will not comment further. Very clever idea.
I imagine the ring aerodynamically performs well with forward flight climb/descent and with gusts?
Based on the model it is possible to produce a rotor giving as much lift as a 22 having 5 times the inertia and being a little over half its weight.
You may have hit the timing right on the head. Sikorsky will soon be demonstrating the X2, which is based on rigid rotor technology. Once you have test data to prove out your idea, i would seriously consider approaching them for either a technology development or licensing budget. I really can't comment about other manufacturers, since i gained any heli knowledge from the "local" Sikorsky representative.
Mart
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whats this then
Graviman. Thanks again for the positive observations. As you rightly say, all the prototypes and theoretical modelling only gives a rough idea of wether in the real world it will work. The only way foreward is to make a full size prototype and try it for real. If anyone out there has nice deep pockets then give me a call! The plan is to have a full size version on test, mounted on the homebuilt Bug3 by late summer next year. Thanks Bug.
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Originally Posted by BugDevHeli
The plan is to have a full size version on test, mounted on the homebuilt Bug3 by late summer next year.
Since Bug3 uses proven R22 components, you need to be at least as convinced about reliability of your components as these. Regularly inspect the ground test prototype for cracks, i don't know what techniques exist for composite. I would suggest strain guaging stess hotspots, but don't know if kit exist to get strain data to static receiver. The idea is you can correlate ground accelerated durability test hours to actual flight hours (normally stress PSDF vs freq is compared). If there should be a design defect, you will detect it well before it puts anyone at risk. The flying prototype can then concentrate on performance development to begin with. This will also help the money men gain confidence in your product.
I imagine you have used some FEA code? I use I-deas for my day job, but wouldn't recommend it!
Mart
Last edited by Graviman; 10th Dec 2006 at 14:45. Reason: Typos
